Image-guided surgery systems use a position sensor system to graphically overlay an iconic representation of a tracked surgical instrument onto pre-acquired images (e.g., CT, MR, fluoroscopic X-ray or other images) of the patient. Current state of the art tracking employs optical systems characterized by a high degree of accuracy. However, the ergonomics of these systems are poor, and optical systems require that tracked objects remain in the camera's line of sight, relatively distant from the instrument tip. The relatively heavy and large position-indicating elements must be attached to rigid instruments to achieve the required accuracy. In particular, maintaining a line of sight path can be cumbersome for the physician and complicate the already delicate operating environment. Together, these drawbacks may lower the acceptance of computer-assisted surgery among physicians.
A new generation of electromagnetic trackers, with increased accuracy and the ability to track objects in ferromagnetic environments, is becoming available. Electromagnetic tracking systems do not require that a direct line of sight be maintained. In addition, these new generation electromagnetic trackers (“position sensors”) use position-indicating elements that are extremely small. The systems normally consist of a control unit, sensor interface device, and field generator. The position-indicating elements consist of small coils that connect to the sensor interface unit.
Image guidance workstations for use in spine surgery have been commercially available for over a decade. These existing CAS workstations are based on optical tracking systems, which do not allow accurate tracking of flexible instrumentation. Flexible instrumentation is generally smaller and less invasive than rigid instrumentation. Current minimally invasive CAS techniques have been limited to rigid instruments due to the tracking technology.
K-wires in general are known. In present clinical practice, K-wires are an essential part of many orthopaedic procedures including spinal fusion, fracture fixation and stabilization. K-wires can also serve as a guides or “trials” for screw placement during instrumented fixation. In some surgical procedures, the K-wires are used to stabilize or manipulate the bones. In others, cannulated screws may be inserted over the K-wire and placed through the bone either to serve as anchor points for plates or stabilizing hardware, or to unite a fracture. The K-wire may be removed or left in place at the end of the procedure. Other uses are possible.
Any misplacement of the K-wire can result in misplacement of the screw or misalignment of a fracture, with potentially catastrophic consequences for the patient. For example, if the K-wire is placed through a critical structure such as a nerve or blood vessel during a spine operation, paralysis or death could result. Misplaced wires can result in decrease in integrity of the fusion or reduced strength of any construct. K-wires are often inserted percutaneously into the bone making it difficult to know where the wire is going without constant x-rays.
One of the drawbacks of conventional image-guided surgery is that the instrument that is actually tracked is usually the holder or driver of the inserted tool. For example, K-wires are often tracked by tracking the drill or a drill guide used to install them, which is proximal to the end actually inserted in the patient. While the tip of a stiff or rigid instrument may remain static with respect to the tracker, a thin proximally tracked K-wire might easily bend during drilling or placement, rendering a trajectory-based on the proximally placed tracker prone to error. This deviation may be easily overlooked as it may occur unless constant imaging is used or the position of the wire is directly and continually viewed by the physician. This later option is essentially impractical in minimally invasive surgery however.
Also, given the static nature of the backdrop projection images in image guided surgery, this error would not be detected during a conventional image guided surgical procedure until a fluoroscopic view is taken.
Other problems and drawbacks exist with known systems and techniques.